Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

8.2 Measurement of Time 209

The latitude varies from 0 (equatorial plane) degrees to 90 degrees north (North Pole) and from

0 degrees to 90 degrees south (South Pole).

The need for time zones was not realized until the latter part of the 19th century when the

railroad companies were expanding. The railroad companies realized a need for standardizing

their schedules. After all, 8:00 a.m.in New York City did not correspond to 8:00 a.m.in

Denver, Colorado. Thus, a need for a uniform means to keep track of time and its relationship

to other locations on the earth was born. It was railroad scheduling and commerce that

eventually brought nations together to define time zones. The standard time zones are shown

in Figure 8.3.

Daylight Saving Time

Daylight saving time was originally put into place to save fuel (energy) during hard times such

as World War I and World War II. The idea is simple; by setting the clock forward in the spring

and keeping it that way during the summer and the early fall, we extend the daylight hours

and, consequently, we save energy. For example, on a certain day in the spring, without daylight

saving time, it will get dark at 8:00 p.m., but with the clocks set forward by one hour, it will

then get dark at 9:00p.m.So we turn our lights on an hour later. According to a U.S. Department

of Transportation study, daylight saving time saves energy because we tend to spend more time

W U T S R Q P O N Z A B C D E F G H I

STANDARD TIME ZONES

Corrected to April 2001

Zone boundaries are approximate

Daylight Saving Time (Summer Time),

usually one hour in advance of Standard

Time, is kept in some places

Map outline © Mountain High Maps

Compiled by HM Nautical Almanac Office

Z

A

B

C

C*

D

D*

E

0

+ 1

+ 2

+ 3

+ 3 30

+ 4

+ 4 30

+ 5

E*

F

F*

G

H

I

I*

+ 5 30

+ 6

+ 6 30

+ 7

+ 8

+ 9

+ 9 30

K

K*

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L*

M

M*

M†

+10

+10 30

+11

+11 30

+12

+13

+14

N

O

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1

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3

3 30

4

5

6

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U

U*

V

V*

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7

8

8 30

9

9 30

10

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hm hm hm hm hm

‡No Standard Time legally adopted

Standard Time = Universal Time + value from table

X V K L

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180 ̊ 150 ̊W 120 ̊W 90 ̊W 60 ̊W 30 ̊W 0 ̊ 30 ̊E 60 ̊E 90 ̊E 120 ̊E 150 ̊E 180 ̊

M N N O O Z

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M M

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International Date Line International Date Line

R

C

B

B

A

P

R

I

■Figure 8.3 Standard time zones.

Source:Map outline (c) Mountain High Maps. Data Supplied by HM Nautical Almanac Office @ Copyright

Council for the Central Laboratory of the Research Councils. http://aa.usno.navy.mil /faq/docs /world_tzones.html

Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).

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